In general, an analyzer such as an infrared gas analyzer, the larger the quantity of light incident upon a cell from a light source, the higher the detecting sensitivity and the more highly accurate the measurement which is achieved.
Although in general a heating resistor has been used as a light source for such an analyzer, such a light source must not be a so-called point light source because of the resistance generated heat therefrom and the limited useful life. Thus, such a light source has a definite size, which results in the disadvantage that the light from such a light source is scattered, and the quantity of light incident upon the cell is reduced.
Consequently, in a conventional analyzer, as shown in FIG. 5, where a pneumatic detector having a relatively large light-receiving surface is used as a detector 50, the detecting sensitivity has been increased by making the light from a light source 51 incident upon a cell 52 in a manner such that it is confined within a predetermined width. As shown in FIG. 6, where a solid detector having a relatively small light-receiving surface is used as a detector 60, the detecting sensitivity has been increased by collecting the light from a light source 61 by means of a lens 62 having superior permeability to infrared rays, and directing this collected light onto a cell 63. Alternatively, the quantity of light incident upon the cell can be increased by using a laser light source as the light source 61.
In said FIGS. 5 and 6, reference numerals 53 and 54 and 64 and 65 designate electro-magnetic valves provided in reference-gas supply means 55 and 66 and sample-gas supply means 56 and 67, respectively. Reference numerals 57 and 68 designate controllers for controlling the opening and closing of these electro-magnetic valves 53, 54, 64 and 65. Preamplifiers 58 and 69 amplify the output of detectors 50 and 60, respectively.
In the above described prior art analyzer as shown in FIG. 5, since a cell 52 having a large cross-sectional area corresponding to the size of the light-receiving surface of the detector 50 must be used, the volume of the cell 52 is large, in particular in the case of a fluid modulation type gas analyzer as shown in FIG. 5, and a disadvantage has occurred in that the analyzer requires a large amount of gas and is expensive.
In addition, in the analyzer as shown in FIG. 6, a disadvantage has occurred in that it is expensive due to a use of the lens 62 or the laser light source.